The present invention relates to a filter for filtering a suspension under pressure and uncontinuously exhausting a filter cake having a low content of a mother liquor.
In a well-known filter system, a filter cloth is disposed on a filter plate provided on the upper surface of a flat filter medium support, and a cover arranged above the filter plate is brought into tight contact with the circumferential portion of the filter plate. Then, a suspension is supplied under pressure to a space defined between the cover and the filter cloth to carry out filtration. When filtration efficiency is reduced because of stacking of a filter cake on the filter cloth, supply of the suspension is stopped, and pressurized air is supplied to reduce mother liquor content of the filter cake. Then, the cover is separated from the filter plate to remove the filter cake as well as the filter cloth. Further, in another well-known filter system, a long filter cloth is used, and a predetermined length of the filter cloth is moved every time a filtering operation is carried out to thereby remove the filter cake. While the drawn filter cloth on which the filter cake is deposited is sometimes abandoned after one use, it is economically preferred to wash and regenerate the filter cloth for reuse. Therefore, a soft cloth such as non-woven fabric cloth is widely used as the filter cloth from the viewpoints of filtration efficiency and economy. However, when a fixed length of such a soft filter cloth is moved by a filter cloth feeding roller and a filter cloth drawing roller, ununiform expansion and contraction of the filter cloth is apt to occur to create lateral deviation. Even if such deviation is intended to be restricted by guides provided on both sides of the filter cloth, there are only created wrinkles of the filter cloth, and the guides cannot return the filter cloth to a normal position.
To this end, when there occurs deviation of a moving position of the filter cloth, the deviation is conventionally corrected by changing the inclination of the filter cloth drawing roll or friction bars provided on front and rear sides of a filtering position. In a conventional control system, such correction of the deviation is automatically carried out by using a photoelectric sensor for detection of an end portion of the filter cloth to control the inclination of the friciton bars. However, it is impossible to eliminate generation of meandering causing the expansion and contraction of the filter cloth. As a result, an excessive width of the filter cloth is required, and a narrow filtering surface only is unavoidably used, which results in economical disadvantages.